TOPIC: Thru-hull holes, fittings, bells and whistles

So I've been doing a ton of research on here and have some Q's.
engine transom bolts are a definite liability for water intrusion, so I was wondering if anyone oversizes their holes to be filled with resin, and then drill them out at the smaller diameter to avoid water getting into the transom wood. Would this crack and leak anyway or would it last if done carefully with some glass? Every boat I have ever looked at have a bunch of sealant in and around the bolts to seal them, but it looks bad and I bet temporary at best.
Also, my '59 Dorsett Catalina has dual drain holes with thru fittings. Looking for the best way to seal them to the glass. Will this be handled by glassing them in or are they installed/sealed in a freshly drilled hole after the hull is finished.
One more thing on sealing holes... mounting bells and whistles. What type of gasket material is used when mounting horns, lights, cleats and chocks, and how do I make sure the holes and screws are sealed.
I know how a 30 year builder and master carpenter would do it but I want to know how the Glassics Pros do it. Thanks folks.

There were a couple members who discussed drilling out the mounting holes bigger and filling with thickened epoxy a couple years ago here. (I believe it would have to be thickened, straight resin wouldn't have the strength needed?) Makes good sense, as this IS the most common place for water intrusion.

I've had good success with using a light coat of resin on the fresh wood drilled in transoms, then seal the mounting holes with 3M's 5200. Wipe off the excess before it cures, it isn't going to help on the outside of the hole anyway! Drain tubes get the same treatment, as do any mounting holes for hardware, etc.. If applied properly that stuff is bulletproof, and leak-proof IMHO. If you're ever going to plan on disassembling it use 4200, not as permanent but easier to get apart.

Just my way of doing it, everybody has their own opinion on this I'm sure.